Are yellow chromate and yellow passivate the same?

A. Thanks, R. You are correct and your references are correct.

A piece of improper slang that others often use and that I have used as well is 'trivalent chromate' -- whereas there can actually be no such thing because it is an oxymoron -- the chemical meaning of 'chromate is' CrO4 in which the chrome must be hexavalent.

But your clarification doesn't negate the real-world communication problem that whether customers specify 'zinc and yellow passivate' or 'zinc and yellow chromate' we still don't know whether they actually want a trivalent passivate or a hexavalent chromate. Ideally they should offer a specification but they often don't because, being human, at the time of the order they "just want it plated" and no hassles, but at the time of delivery they naturally want it to be exactly what their customer actually wants :-)

Luck & Regards,

A. Hi, Arthur.

I will answer your questions, but need to remind you that copywriters are not there to inform us ... they are there to sell us on whatever they have to offer! Thus, if they are trying to sell their cheaper, thinner and less protective zinc plating against others who are offering thick and corrosion resistant hot dip galvanizing, they invent phrases like "electro galvanized", which they subsequently feel entitled to shorten to "galvanized" (against howls from metal finishers) in order to insert another layer of obfuscation :-)

So, just because we tell you what these words mean to a metal finisher today doesn't mean the copywriters will follow those definitions tomorrow. They'll probably try their best not to :-)

1. Yes, "yellow chromated" and "yellow passivated" are the same -- meaning an electroplated finish (usually zinc plating because it's the least expensive) followed by a chromate conversion coating which shall be yellow in color.

2. "Black finish" doesn't imply anything except the color. Black passivated would mean zinc plating with a black chromate conversion coating. Black oxide is a different finish entirely, but means the same thing as "gun bluing"; it can tend to look matte black on a rough surface but a jewel-like royal blue to navy blue on a highly polished surface. Black oxide offers no corrosion resistance by itself, but depends on the oil or wax on it to retard rust.

3. Passivate is a tricky one because it means different things for different substrates. Passivation of stainless steel is a completely different process than passivation/chromating of zinc plating.

4. Traditional hexavalent chromate is inherently a yellow-ish/honey-ish/amber-ish color. So, in the old days, a dark yellow chromate implied a significantly thicker and more corrosion-resistant coating than a clearer chromate. Today, as a result of RoHS and changing times, trivalent chromate is more common and this is not necessarily yellow. Today a yellow color is often nothing but dye. "Yellow plating" is a somewhat meaningless phrase, but what often happens is "zinc plating with yellow chromate" gets abbreviated as "zinc, yellow" or "yellow zinc" on purchase orders and packing slips.

Regards,

Well said Ted!

A. Hi Amina. I will be happy to confirm that !

... but only if I am also allowed to remark that miscommunication/misunderstanding is the single number one problem in business, and asking a third party what the first party probably meant can sometimes aggravate those miscommunications :-)

Luck & Regards,

A. Hi Adeniyi. Yes, "passivation" of zinc electroplating, and "chromate conversion coating" / "bichromating" / "dichromating" of zinc electroplating are all the same thing. And, yes, it is most often done in clear or yellow color, but can be done in olive green or black as well. Zinc electroplating is virtually never done without it.

However, these days there are RoHS, WEEE, automotive, and other environmental pressures to not use toxic hexavalent chromate, and to employ trivalent chromates instead (the phrase 'trivalent chromate' is actually an oxymoron because the "-ate" implies hexavalent according to chemical naming rules, but the phrase is widely used nonetheless).

So what will be important for you to determine is whether your customer wants a trivalent passivation/conversion coating to comply with environmental standards, or the old fashioned hexavalent chromate. It would actually be best to use specifications like ASTM B633 rather than loose terms like 'zinc plated with yellow or clear passivate'.

Regards,

A. Hi Thomas. You probably read the earlier entries on this page, so I won't repeat them; I'll just summarize that "yellow passivated zinc finish" means zinc electroplating followed by a yellowish chromate conversion coating.

Re. chlorine: no, there is no chlorine involved. The plating solution might be chloride-based, but the chloride itself is no more dangerous than the chloride in table salt.

Re. cyanide content: In the old days of 50 years ago the zinc plating solution was usually cyanide based; today it rarely is. But in any case, the zinc is metal; any cyanide, acid, or anything else used in the process has been neutralized and rinsed off. It was also common until about 20 years ago to lace the chromate conversion coating with a small amount of cyanide, because it accelerated the process. But if you specify "RoHS-compliant trivalent chromate conversion coating" you should have no worries about cyanide, hexavalent chromium, or any other toxin.

What may be a concern is suitability and appearance.. .

Suitability: This is a corrosion resistant finish that you will see on fasteners; brackets, mounting plates, and chassis for electronic devices, underhood and internal parts in automobiles, internal parts in inexpensive door locks and closing mechanisms, hinges (it looks sort of like brass), etc. But if this balustrade is actually a handrail, it will probably not hold up well to abrasion and finger oils and perspiration.

Appearance: This is generally not considered a decorative finish. The reason to note this is that although you might find the "industrial" look of it pleasing, any given look to it might be considered random & coincidental, so for an application like this you will need samples and a sample board of acceptable parts because if, for example, half is done by one company and half by another, the parts may all look generally yellow but terribly different. Good luck.

Regards,

Hi cousin Rod. Thank you very much for such kind words.

Regards,

A. Hi Daniel. Type V is intended to offer the functionality and appearance of Type III, but without using the older traditional hexavalent chromate (the chemical whose toxicity and carcinogenicity made Erin Brockovich a household name). It tends to be higher technology and highly proprietary, and it's not necessarily a drop-in replacement, but the general answer is that the world is rapidly moving towards Type V and phasing out Type III. Good luck.

Regards,

Hi Ted, I've been searching this forum for a while and I can tell you this is a great site. THANKS.